There is currently a large and growing requirement for NF3 in semiconductor manufacturing. One of the early processes for producing NF3 involves the direct fluorination of ammonium ions by F2 whereby gaseous F2 is contacted with liquid (molten) ammonium acid fluoride (AAF) in a stirred tank reactor. The early processes operate at a molar ratio of HF to ammonia of 2.0 to 2.5 (melt ratio) in the reaction liquid and at temperatures above the melting point of ammonium bifluoride, NH4HF2, which is 127° C. Later processes for producing NF3 effect the direct fluorination of ammonium bifluoride using higher HF/NH3 melt ratios.
The following patents and articles describe processes for production and purification of NF3.
U.S. Pat. No. 4,091,081 discloses an early process for the production of NF3 by the direct fluorination of ammonium bifluoride at temperatures above 260° F. and below 400° F. in a stirred tank reactor. An HF/NH3 ratio of 2 to 2.5 is maintained.
U.S. Pat. No. 4,156,598 discloses a process for the production of NF3 by the direct fluorination of ammonium bifluoride. To extend the life of the adsorber columns employed in the NF3 purification process, N2F2 is removed to a level below 0.03 volume percent before there is adsorption of N2O and water from the reaction product.
U.S. Pat. No. 5,637,285 discloses the production or NF3 by the direct fluorination of an ammonium source, e.g., ammonium bifluoride employing a melt ratio of HF/NH3 of at least 2.55 and a power input to the reaction medium of greater than 1000 watts per cubic meter of reaction medium. Representative ammonium source reactants disclosed for NF3 production include compounds of the formula NH4Hx−1Fx(NH4)yMFz.nHF where x is greater than 2.55; y is 1–4; z is 2–8, and n is sufficient to maintain the reactant as a liquid. The patentees acknowledge that more HF byproduct is produced by this process than in low melt ratio prior art processes, but point out that a portion of the HF can be recovered and recycled. The patentees also note that even though higher melt ratios are employed, low levels of waste melt (1.35 lbs of ammonium acid fluoride per lb of NF3) can be achieved, which level of waste melt is considerably lower than the levels which could be achieved by the process disclosed in U.S. Pat. No. 4,091,081.
US 2003/152,507(A1) discloses a process for producing NF3 using a heat engine cycle with an NF3 reactor to eliminate or greatly reduce the need for mechanical energy input derived from stirrers or turbines employed in the past without sacrificing high F2 to NF3 conversion rates. In one aspect, the reactor comprises a mixing zone and a reaction zone wherein HF is passed through a vapor jet. Mechanical energy is generated using the working fluids HF and NH4F(HF)x which are capable of undergoing cyclic compression and expansion.